Support core ribbon for cold-shrink tube

ABSTRACT

A core for an elastomeric tubing assembly is produced from a ribbon helically wound on itself to form a cylindrical tube. The edges of the ribbon are formed to interlock with each other and are contoured to facilitate ultrasonic welding of the edges. A support member is coextruded in the ribbon to provide increased resistance to premature collapse of the tube.

FIELD OF THE INVENTION

This application is a continuation-in-part application of U.S.application Ser. No. 08/384,516, filed on Feb. 6, 1995, now U.S. Pat.No. 5,670,223. This invention relates generally to elastomeric sleevingsupported by a removable core, and particularly to construction of thecore.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,515,798, assigned to the assignee of the presentinvention, describes an elastomeric cover and removable core assemblywhich is particularly useful in the electrical distribution industry.However, the application of rubbery insulating sleeves to electric wireor cable splice areas is illustrative, and although the invention willbe described primarily in terms of devices and procedures adaptedparticularly therefor, it is not to be construed as limited thereto,being equally applicable, for example, in the application ofcorrosion-preventing protective sleeves to welded pipe joints. Theassembly is typically referred to as cold shrink tubing to differentiateit from polymeric tubing which may be shrunk by the application of heat.

FIG. 1 illustrates a typical use for and construction of a cold-shrinktube assembly and shows two cable-ends 11 comprising a strandedconductor 12 and an insulating covering 13. The covering is cut away at14 and the conductors 12 joined together in end-to-end configuration bysuitable means which may typically consist of a compressed or indentedmetal sleeve or a close-fitting metal tube with set-screw insulatingmastic or tape, here omitted for clarity of illustration.

The cold-shrink tube assembly is slipped over one of the wire-ends priorto joining the two ends. After the splice is completed, the assembly isslid into position over the splice area and the support is removed topermit the elastic cover to contract and form a tight fit. The processwill be apparent from the illustration. The support comprises a unitarytubular core 15 helically grooved along its entire length, thecontinuous groove 16 permitting the core 15 to be pulled out into acontinuous strip 17 which is removed through the bore, i.e., frombetween the core and the cable 11. An elastic tube 18 in radiallyextended or stretched condition is supported on the core 15. As thestrip 17 is progressively withdrawn, the tube 18 contracts about thecable as at 19 to form a closely conforming and tightly retainedprotective covering. Contraction of the tube results in the applicationof a resultant force against the end of the core 15 and assists in theremoval of the strip 17 as the core 15 is unwound.

Although the construction described above has been used effectively formany years, considerable effort has been invested to reduce the amountof material used for the core 15 without compromising the strength ofthe core 15, i.e., its ability to withstand the compressive forcesimposed upon it by the elasticity of the tube 18.

One method of reducing the amount of material used in the core 15 hasbeen to produce the core 15 from a continuous ribbon 20 such as thatshown in FIGS. 2 and 3. The ribbon 20 includes edges 22 and 24 whichinterlock, as shown in FIG. 3, when the ribbon 20 is helically wound toform a tubular core. The interlocked edges 22 and 24 may be joined bysuch means as adhesives, heat welding or solvent welding, but thepreferred method is ultrasonic welding. The construction of FIGS. 2 and3 was effective to reduce the amount of material used in the core 15since the thickness of the core tube could be reduced as it was nolonger necessary to cut a groove 16 in the material to form the helicalline of weakening which allowed the core 15 to be pulled as a strip 17from the assembly. The joint between the edges 22 and 24 of the joinedribbon 20 formed the helical line of weakness around the core 15.Unfortunately, it was found that the extensive surface area of thecontact between the two edges 22 and 24 of the ribbon 20 resulted inbonds at the joint surface which were difficult to control, both interms of location and strength. As a result, the core 15 was at timestoo weak to support the elastomeric sleeve 18 or too strong to alloweasy stripping of the core 15 from the sleeve 18.

The present invention modifies the shape of the ribbon edges 22 and 24in order to achieve greater uniformity of bonding at the joint.

As less material is used in the support core, the possibility ofpremature collapse increases, especially as the diameter of the corebecomes larger. The support core must have strength sufficient to resistcollapsing under the compressive force of the tube for long periods oftime and at elevated temperatures. The external pressure of the tube cancause collapsing of the support core, for instance, by buckling. Thiseffect can be enhanced by the uneven thickness of the expanded tubewhich results in uneven pressure on the support core. Subject to thisuneven pressure, the support core takes on an oval shape which is easierto collapse than a perfect circular cylinder. Ellipicity is the mostimportant defect which determines premature collapse of circularsupporting tubular cores. As the diameter of the support cores andexpanded elastic tubings increases, the defects may become morepronounced and thus make premature collapse more common. Further, forgiven materials, the thickness of support cores required to supportlarge diameter expanded elastic tubings is a fast function of thediameter of the core. Hence, there has been a natural limit to the sizeof tubings which can be reliably supported by collapsible support coreswithout the wall thickness of the core becoming unacceptably large.

The invention provides a ribbon with greater hoop strength by placingwithin the ribbon a support member formed of a material capable ofwithstanding high temperatures and increased pressure associated withlarge diameter support cores and stretched elastic tubings.

SUMMARY OF THE INVENTION

The present invention produces cold-shrink tube assembly cores havingmore uniform and predictable characteristics than previous coreconstructions. The core is manufactured from a ribbon adapted to be edgejoined to itself to form a helically wound tube. The ribbon comprises alongitudinal body having first and second major surfaces and first andsecond edges. A support member extends longitudinally through the bodyof the ribbon. The ribbon additionally comprises a first couplingprojection extending from the first major surface toward the secondmajor surface and terminating short of the second major surface, asecond coupling projection extending from the second major surfacetoward the first major surface and terminating short of the first majorsurface, recesses in the short of the first major surface, recesses inthe ribbon adjacent the first and the second coupling projections foraccepting the projections and thus permitting the first couplingprojection of one ribbon section to engage the second couplingprojection of another ribbon section with the major surfaces of theribbon sections aligned to form a smooth surface of the tube, thecoupling projections being formed such that the first and the secondcoupling projections may engage each other along a continuous surfacefree of any surfaces which are perpendicular to said major surfaces.

The support member within the body of the ribbon may be a coextrudedpolymer, such as ABS resin or modified PPO resin. The support membergives additional hoop strength to the ribbon such that the core is moreresistant to premature collapse when subjected Lo high pressuresassociated with large diameter stretched elastic tubes, or when storedin high temperature conditions.

The ribbon may further include perforations within the larger recess toalternatively or additionally increase the uniformity of the forcenecessary to separate the helical coils of the core when it is desiredto remove the core from the sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more particularly described with respectto the following drawings, wherein like numbers refer to like parts inthe several views, and wherein:

FIG. 1 is plan view, with portions in cross-section, of a cable andprotective sleeve assembly of the prior art;

FIG. 2 is a cross-sectional view of a ribbon used to manufacture atubular core according to the prior art;

FIG. 3 is a cross-sectional view of the ribbon of FIG. 2 wound inhelical fashion and edge-joined to manufacture a tubular core accordingto the prior art;

FIG. 4 is a cross-sectional view of a ribbon used to manufacture atubular core according to the present invention;

FIG. 5 is a cross-sectional view of the ribbon of FIG. 4 wound inhelical fashion and edge-joined to manufacture a tubular core accordingto the present invention.

FIG. 6 is a cross-sectional view of the ribbon of FIG. 4 showing asupport member within the body of the ribbon.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 2 and 3 illustrate a ribbon 20 of the prior art from which atubular core similar to the core 15 of FIG. 1 may be wound. The ribbon20 includes formed edges 22 and 24 which allow one edge 22 of onelongitudinal portion of the ribbon 20 to interlock with the oppositeedge 24 of another longitudinal portion of the ribbon 20 so that theribbon 20 may be helically wound to form a cylindrical tube. This tubemay be used as a core to support an elastomeric sleeve of rubber orother suitable material as shown in FIG. 1.

As the ribbon 20 is helically wound, the edges are joined by a suitablemethod, such as by means of an adhesive, heat welding or solventwelding, but preferably ultrasonic welding, to provide sufficientstrength in the finished core to support the sleeve in an expandedstate. At the same time, it is desirable that the strength of the jointbe sufficiently weaker than the strength of the ribbon 20 material sothat the joint will separate predictably when it is desired to tear thecore into a strip to effect its removal from the sleeve.

It has been found that the configuration of the edges 22 and 24 of theribbon 20, and the resulting length of the line of contact between themated edges, did not always allow the results of welding or bonding tobe accurately predicted, either in the location of the weld along theline of contact between the halves or in the strength of the bond. Inparticular, it was found that the vertical surfaces associated with theconstruction of FIGS. 2 and 3 caused undesirable and unpredictablewelding or bonding at these locations. This at times resulted in tearingof the material of the ribbon 20 rather than separation at the joint,insufficient strength to support the elastomeric sleeve or undesirablyhigh effort necessary to separate the core into a strip for removal.

FIGS. 4 and 5 illustrate a ribbon 30 designed to minimize theuncertainties associated with the ribbon 20 of FIGS. 2 and 3. The ribbon30 is of any polymeric material suitable for ultrasonic welding or otherbonding techniques and possessing sufficient strength to support thesleeve. Suitable materials have been found to be polyolefins. The ribbon30 includes asymmetrical edges 32 and 34 which are designed to providegreater control over bonding in general, and, in particular, ultrasonicwelding of the ribbon edges 32 and 34 to each other. Each edge 32 and 34includes a coupling projection 36 and 38 extending from a major surfaceof the ribbon 30 to a point short of the opposite major surface of theribbon 30. Each coupling projection 36 and 38 includes a contour whichresults in surface contact around substantially the entirety of theprojection 38 without any vertical mating surface between the projection38 and the projection 36.

Each coupling projection 36 and 38 is received by a recess 40 and 42which are shaped to control contact between the mated edges of theribbon 30. At least one of the recesses 42 is preferably oversized inrelation to its respective coupling projection 36 so that an open areais produced adjacent the coupling projection 36 when the couplingprojection 36 is inserted in the recess 42. In this manner, the extentof contact between the coupling projections 36 and 38 and the recesses40 and 42 is controlled, thus allowing further control over the bondingprocess used to join the ribbon edges 32 and 34.

As shown in FIGS. 4 and 5, the ribbon 30 may be formed with a continuousperforation 44 extending from the bottom of the larger recess 42 throughthe ribbon 30 to exit at the major surface of the ribbon 30. Thisperforation 44 may be used to control the force necessary to separatethe core into a strip for removal. For example, the weld between theedges 32 and 34 of the ribbon 30 can be increased to a high strengthlevel by appropriate selection of edge 32 and 34 contours, but thestripping force can be maintained at lower predetermined levels byproper selection of perforation size and the separation between adjacentperforations.

As shown in FIG. 6, the body of ribbon 30 may be provided with a supportmember 50. Support member 50 extends longitudinally along the length ofribbon 30. Support member 50 preferably has greater strength andtemperature resistance than the material forming the remainder of ribbon30, such that the inclusion of support member 50 in ribbon 30 causes asupport core formed from ribbon 30 to exhibit increased resistance topremature collapse when subjected to high pressures from large diameterstretched elastic tubes and when stored in high temperature conditions.Support member 50 is preferably a thermoplastic material, such as ABSresin (a terpolymer based on acrylonitrile, butadiene and styrene),while the remainder of ribbon 30 is formed of a thermoplastic materialsuch as a polyolefin resin. Other suitable materials for support member50 include, for example, a modified PPO (polyphenylene oxide)resin.Support member 50 is preferably coextruded with the body of ribbon 30.However, other methods of forming ribbon 30 with support member 50 asshown in FIG. 6 may be recognized by those skilled in the art, and arecontemplated to be within the scope of the present invention.

The improved strength of a core formed from a ribbon 30 as depicted inFIG. 6 can be seen from the data in Table 1. The data in Table 1 wasgenerated by forming cores from three types of ribbon: 1) polyolefinwith no support member (POLY); 2) polyolefin coextruded with an ABSresin support member (CO-ABS); and 3) polyolefin coextruded with amodified PPO resin support member (CO-PPO). The core internal diameterwas measured and the core was placed on its side in a test fixture in a70° C. oven. The sample was left in the oven for 10 minutes. Ten minutesinto the test, weight was placed on top of the sample and the core innerdiameter measured. Additional weight was added and the inside diametermeasured at ten minute intervals until the core had collapsed to an ovalshape having an inside diameter 2/3 of the original diameter, at whichpoint core failure was deemed to have occurred. All core samples had awall thickness of 0.1 inch.

                  TABLE 1    ______________________________________            Initial     Failure    Core      I.D.          time   weight    Material  (mm)          (min)  (lbs.)    ______________________________________    POLY      46            30      5.39    POLY      68            40      8.08    CO-ABS    47            70     16.16    CO-ABS    61            40      8.08    CO-ABS    68            80     18.85    CO-ABS    68            60     13.47    CO-PPO    61            50     10.77    CO-PPO    69            50     10.77    ______________________________________

As seen in Table 1, when comparing cores of similar initial diameters,those cores formed from a ribbon having a coextruded support member ofeither ABS or modified PPO performed significantly better than the coresformed from a ribbon lacking a support member. In particular, the coreshaving the support member took longer to fall and failed at higherweights than the cores without a support member.

Although the present invention has been described with respect to only asingle embodiment of coupling projections, many modifications will beapparent to those skilled in the art. For example, both recesses 40 and42 may be oversized with respect to the coupling projection 36 or 38which is to be inserted therein. Also, although only a single projectionand recess is shown at each edge of the ribbon, it is possible to havemore than one projection on one or both edges, with recesses separatingeach projection. In this manner, any number of "fingers" could lock theedges of the ribbon together. Similarly, although support member 50 isshown as rectangular in shape, other shapes and configurations ofsupport member 50 would work equally well.

What is claimed is:
 1. A ribbon adapted to be joined to itself to form ahelically-wound tube, the ribbon comprising:a longitudinal body havingfirst and second major surfaces and first and second edges; a supportmember extending longitudinally through the body; a first couplingprojection extending from said first major surface toward said secondmajor surface and terminating short of said second major surface; asecond coupling projection extending from said second major surfacetoward said first major surface and terminating short of said firstmajor surface; recesses in said ribbon adjacent said first and saidsecond coupling projections for accepting said projections and thuspermit said first coupling projection of one ribbon section to engagesaid second coupling projection of another ribbon section with the majorsurfaces of said ribbon sections aligned to form a smooth surface onsaid tube; said coupling projections being formed such that said firstand said second coupling projections engage each other along acontinuous surface free of any surfaces which are perpendicular to saidmajor surfaces, at least one of said recesses being larger than thecoupling projection to be inserted therein so that an open area isprovided adjacent said coupling projection when said coupling projectionis inserted within said one recess.
 2. The ribbon of claim 1, whereinthe body and support member are formed of thermoplastic materials. 3.The ribbon of claim 2, wherein the body and support member arecoextruded.
 4. The ribbon of claim 3, wherein the body is formed of apolyolefin resin and the support member is formed of ABS resin.
 5. Aribbon according to claim 1 further including spaced perforationsextending through said ribbon at said one recess.
 6. An elastic sleeveassembly comprising an elastic sleeve member supported in highlystretched condition on a hollow core formed of a ribbon adapted to bejoined to itself to form a helically-wound tube, the ribbon comprising:alongitudinal body having first and second major surfaces and first andsecond edges; a support member extending longitudinally through thebody; a first coupling projection extending from said first majorsurface toward said second major surface and terminating short of saidsecond major surface; a second coupling projection extending from saidsecond major surface toward said first major surface and terminatingshort of said first major surface; recesses in said ribbon adjacent saidfirst and said second coupling projections for accepting saidprojections and thus permit said first coupling projection of one ribbonsection to engage said second coupling projection of another ribbonsection with the major surfaces of said ribbon sections aligned to forma smooth surface on said tube; said coupling projections being formedsuch that said first and said second coupling projections may engageeach other along a substantially continuous surface free of any surfaceperpendicular to said major surfaces, at least one of said recessesbeing larger than the coupling projection to be inserted therein so thatan open area is provided adjacent said coupling projection when saidcoupling projection is inserted within said one recess.
 7. The assemblyof claim 6, wherein the body and support member are formed ofthermoplastic materials.
 8. The assembly of claim 7, wherein the bodyand support member are coextruded.
 9. The assembly of claim 8, whereinthe body is formed of a polyolefin resin and the support member isformed of ABS resin.
 10. A assembly according to claim 6 furtherincluding spaced perforations extending through said ribbon at said onerecess.